among us with the least. Almost 500,000 people who call the streets home. Their meals? Whatever they can find, whatever they are given. Can you help me out? Reporter: What would you do if you saw a good samaritan give a homeless man $20 for a bite to eat. Get whatever you want, okay? Reporter: Only to see him tossed back to the curb, the second she leaves? It's bad for business. I can't let you sit in here. Reporter: A man, denied service, simply because he's homeless. Today, we've brought our hidden cameras to the streets of lynbrook, New York, and Mcquade's restaurant. Of course, both Traci and Kevin are actors. And the bartender, Jeremy? It's not your money, get out of here. Reporter: He's definitely an actor. Everyone at this bar knows it, except this man. And our hidden cameras are rolling. Oh wow, it's nice in here. This is a friend of mine, do you have a menu or something he can look at? Just get whatever you want. Here's $20. That's really nice. Reporter: Right away, he takes notice, but as soon as Traci leaves, Jeremy has a change of heart. Listen, man, they have places you can go, like a soup kitchen or something. I am paying customer, look. I mean, I've got $20. That's not your money. I don't want you bothering these paying customers. I'm not bothering anybody. Am I bothering you? He is being polite. Reporter: Oleh babski has seen enough. Yeah, but you took his $20. It was not his $20. His $20, she gave it to him for him to eat. I heard it. Okay, but if I give this $20 back to him, what's he going to do? Whatever he wants, it's his money. He's going to go buy liquor He wants to eat. That's what he is looking for. Reporter: We've barely begun here, but already a bold move. Who are you calling? The police. You're calling the police on me? Yeah. Reporter: He makes it clear to Jeremy it's meal or no deal. Give him back the $20. Thank you. Reporter: Not everyone is quite so welcoming. Uh-oh, he's got a homeless guy outside. Reporter: But now the homeless guy is inside. These two women don't want a homeless man seated anywhere near them. These ladies, and I can smell you too. Reporter: And Jeremy offers an alternative. He's bothering you right? Sorry about that. I hope that didn't ruin your appetite. Reporter: Tough day for Kevin. These two men also give him a cold shoulder. I'm just trying to get something to eat. Reporter: They won't even look him in the face. Excuse me. Imagine you're down on your luck. Reporter: With the pleas falling on deaf ears, we tell Kevin to leave. Sorry, guys. You feed him once, there's 20 guys out here. Reporter: They agree with Jeremy. Why? Buy a sandwich somewhere. Reporter: But not here? Wrong place. Reporter: And as this next man walks in, things only get worse. Run him through the dishwasher in the back. Just want to get a little bit of food in me. Don't cough on everything. Reporter: With Jeremy, they literally laugh at his misfortune. Can I please get a sandwich? Oh, my god. Give the guy a couple of croutons that are on the floor in the kitchen or something. I am a paying customer, man. I don't work in a soup kitchen. I work in a bar, okay? Reporter: It seems like he couldn't care less about our homeless man, but then he realizes there's more at stake here. Can you give me my money back then? You confiscated his money? I'm not going to give you the money back. Give the guy his money, you got to give him his money back You going to buy booze with this? No. Reporter: Now watch what happens when Kevin leaves the restaurant. I just don't think homeless people should be allowed in bars, you know. How did he end up here? He wasted his money. Well, I mean, we don't know that, we don't know that. He looks like a decent guy. Reporter: A decent guy, and as it turns out, so is Anthony Gambino. Do me a favor, make the guy a sandwich and put it on my bill, all right? Make him a sandwich? Make him a sandwich. Okay. Kevin, you're still standing by out there right? Yeah. Reporter: This guy just said he wants to buy you a sandwich You're kidding me, that guy? Okay, what kind of sandwich should I get him? Turkey burger? Turkey burger? Nah, he needs something a little more than that. That's for weight watchers. Get him the short skirt steak tacos. A lot of protein in that? 100%. Reporter: And now Anthony, who seconds ago was insulting Kevin, hand-delivers his meal. Hungry? Here you go, pal. Are you serious? Thank you. Reporter: Before he buys him a round of drinks, time to introduce ourselves. . Reporter: You started off joking with the guy. Yeah, I was messing around with him. I wanted to rile him up a bit. Reporter: And then you wind up doing something that totally surprised us. You know, I've have had some hard times in my life and, you know, other people were there for me, you know? So I try and do the same thing. Reporter: Paying it forward. This next man understands that concept all too well, as soon as he sees Kevin on the street. Thanks, bud. Just hit right here. Reporter: Seconds later, Kevin is seated right next to him. I don't want you bothering anybody, I don't want you bothering this nice man. He didn't bother me. Thank you. Why don't you have some soup? You've never been there? I work. We all work. Some of us hit bad times. Can I get like a glass of water? Just water. You want the free thing on the menu? Reporter: A small request, that leads to a touching moment. Thank you. Now you're making him give you his drink. No, don't worry about it. Thank you. You're welcome. To your health. To yours, too. And better times. Reporter: But from Jeremy, the insults just keep getting worse. I am sure there's a hose out there somewhere. You don't have to be cruel, man. You want me to be cruel? Get out of here. Hope you enjoyed your water. Why'd you take the money, buddy? You know what he is going to do? He's going to buy drugs and alcohol. He may, but you can't take that money from him. You take the money from him and you are stealing. And I will make sure you get arrested for it. Why are you defending a homeless guy? Because you are a ! Reporter: Kevin leaves. I hope I did the right thing. No, you didn't. Reporter: Arnie Gerber is full of emotion. You think I did something wrong? You've never had anything happen to you that you wish didn't, or that you wish you could get out of? Reporter: It's a message that's very personal to arnie you said to him, "Haven't you ever been through hard times?" Well, haven't we all? Everybody has been through hard times. You survive in some way. And if somebody helps you, and gives you a push up, fine. Reporter: Almost half the people we met this day did just that. They spoke up for a hungry stranger, down on his luck. Heroes? They don't think so. Heroic is the guy that landed the plane in the Hudson river, that's heroic. Wouldn't anybody else do the same thing?

This transcript has been automatically generated and may not be 100% accurate.

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